Research On Compliance Control Method For Underwater Gripper

Underwater manipulator is an important tool for the underwater robot to directly interact with its environment and complete tasks.For the tasks that require force control,the underwater manipulator should possess active compliance ability.In contrast with the air environment,the underwater environment is more complex,with the influence of water resistance and random disturbances.As a kind of classical compliance control method,the force tracking ability of the impedance control method in the underwater environment is not as good as in the air environment.On the basis of the impedance control method,simulations and experiments of the force tracking ability of an underwater gripper were conducted in the thesis.The dynamic model of the underwater manipulator was established,and the force of the water environment on it was analyzed.The mechanical analysis when the target object is grasped was discussed,and the influence of the underwater environment is consist of the direct effect on the gripper and the indirect effect of the disturbance force transferred to the gripper by the target object.The problems of position based impedance control in the underwater environment were analyzed.The simulation model was built based on Simulink platform,and the influence of impedance parameters on the system was discussed.Simulations of position based impedance control were carried out by introducing the estimation error of the target object’s position and stiffness as well as the influence of the disturbance force in the underwater environment.In order to solve the problems of position based impedance control in the underwater environment,a stiffness-adjustment adaptive impedance controller and a parameter identification self-correcting impedance controller were designed.Both of the controller models were built based on Simulink,and simulations showed that both of them could solve the problems.Then the more suitable one for underwater compliant grasping task was determined by further simulation.A layered motion control system consisted of a host computer,a control layer and an executive layer was designed,and an experiment platform for underwater grasping was built.The force sensor was calibrated and the underwater impedance control grasping experiment was carried out.It was verified that the controller had a good performance on the force tracking grasping task in the real underwater environment.